Cracking Eggshell Problems in Ageing Layer Hens
'500 eggs per hen housed' is the new standard in the layer industry. Although the increase in the number of eggs per productive hen has improved the sustainability of egg production (because fewer pullets need to be raised to achieve the same number of eggs), eggshell quality remains a concern to the industry. This is especially true in older hens, because of how their bodies utilize critical nutrients like vitamin D and calcium.
Addressing the eggshell quality issue is critical for reducing the waste represented by broken eggs and increasing the number of saleable eggs. However, it requires an understanding of the interplay of various factors, including eggshell structure and calcium metabolism. To help unpick these different factors and empower the layer industry with the knowledge to take on the eggshell quality issue, Swiss animal nutrition experts in Herbonis have recently released the collaborative work Eggcellent: Cracking Eggshell Quality in Ageing Layer Hens. Today, five contributors to the free book — Dr. Maxwell Hincke of the University of Ottawa, Dr. Wayne Bryden of the University of Queensland, and Herbonis Animal Health’s Dr. Jan Dirk van der Klis, Dr. Kathrin Bühler, and Dr. Sabrina Autzen — summarise some of the most important takeaways.
Dr. Jan Dirk van der Klis
Head of the R&D and Technical Services
Herbonis Animal Health
[Feedinfo] Dr. van der Klis, can you start by introducing the role of calcium and vitamin D in the eggshell quality question?
[Dr. Jan Dirk van der Klis] Eggshell quality is linked to eggshell structure and to calcium metabolism. The calcium turnover in a productive laying hen is one of the most active observed in any animal, as laying hens deposit the equivalent of 10% of their body calcium store into the eggshell every day. However, the efficiency of calcium absorption from the gut is reduced with age, which impacts bone and eggshell quality. Understanding these effects is crucial to be able to compensate for them in the ageing hen.
It was shown a few decades ago that changes in vitamin D metabolism are key. The efficiency of transforming vitamin D into its bioactive form is reduced with hen age, because of the reduction in activity of an essential kidney enzyme required for vitamin D metabolism. Recent studies with modern breeds corroborate these results, demonstrating that the activation of vitamin D or 25(OH)D is compromised in modern laying hens, too.
Increasing dietary calcium levels with age is not an effective solution in the absence of adequate levels of the active form of vitamin D. Excess calcium in the gut that is not absorbed might even complex with other nutrients, reducing their digestibility too. Moreover, the structure of the eggshell also changes with age, affecting its characteristics. Therefore, it is necessary to come up with alternative strategies to increase egg production of first-class table eggs during the whole laying cycle, to fully utilize the benefit of the increased genetic potential of the modern laying hen and to further improve the sustainability of the egg industry.
Dr. Maxwell Hincke
Professor, Department of Cellular and Molecular Medicine
University of Ottawa
[Feedinfo] Dr. Hincke, in what structural ways do shells from eggs laid by older hens differ from those laid by younger hens?
[Dr. Maxwell Hincke] This is an excellent question. Eggshell quality deteriorates with hen age during the production cycle, in spite of careful attention to feeding regime, housing, and environment, and has been the subject of intense genetic selection by producers. Although a laying hen apparently can maintain the concentration of blood calcium ions over time, eggs laid by older hens exhibit modifications in eggshell ultrastructure and microstructure characteristics (i.e., type B mammillary bodies, mammillary density, size of calcite crystal units) that are associated with the marked decrease in eggshell mechanical properties. Such changes in eggshell ultra- and microstructure characteristics are thought to be responsible for the marked decrease in eggshell breaking strength in eggs from older hens as far not explained by the observed reduction in eggshell thickness.
[Feedinfo] Do we understand why that is the case?
[Dr. Maxwell Hincke] Altered uterine gene expression of certain eggshell matrix proteins in the late phase of production, resulting in modified uterine fluid protein composition, is believed to contribute to the age-related alteration in eggshell ultrastructure and inferior mechanical properties. Interestingly, forced molting of aged hens, which regenerates oviduct tissues, results in partial restoration of eggshell strength, and reverses changes in shell structure. Moreover, certain eggshell matrix proteins are present in higher concentrations in eggshell from molted hens compared to hens that are not molted, while others are less abundant.
Dr. Wayne Bryden
Queensland Alliance for Agriculture and Food Innovation
University of Queensland
[Feedinfo] Dr. Bryden, why do you say that increasing dietary calcium concentrations in the second half of lay to maintain eggshell quality is “a simplistic approach to a complex area”?
[Dr. Wayne Bryden] Eggshell formation involves complex interactions between the intestines, kidneys and bone to ensure an adequate amount of calcium is in the uterus (shell gland) for eggshell synthesis. These interactions ensure calcium homeostasis and are mediated by hormones (including vitamin D) along with dietary and circulating concentrations of calcium and phosphorus. Due to the dynamic nature of these interactions, simply increasing dietary calcium without adjusting phosphorus and vitamin D concentrations may perturb calcium homeostasis and reduce eggshell quality.
Moreover, there is another layer of complexity. Particle size of the dietary calcium source is important as larger particles help maintain both eggshell quality and bone strength.
[Feedinfo] How are too high levels of dietary phosphorus a contributing factor to decreased eggshell quality and bone quality in older birds?
[Dr. Wayne Bryden] About 60% of the calcium required for eggshell formation comes from the diet, with the remainder from bone resorption. As calcium is stored in bone, together with phosphorus, bone resorption increases both serum calcium and phosphorus contents. Where calcium is needed for eggshell formation, phosphorus is excreted via the kidney under control of a hormone FGF23. This hormone also reduces the activity of 1a-hydroxylase in the kidneys. Too high dietary phosphorus levels have similar effects. Reformation of bone lost during eggshell synthesis requires both calcium and phosphorus in an optimum dietary calcium/available phosphorus ratio. When dietary phosphorus concentrations are too high, this can perturb bone metabolism and interfere with the availability of calcium for eggshell formation.
Dr. Kathrin Bühler
Lead R&D – Animal Sciences
[Feedinfo] Dr. Bühler, how is vitamin D connected to calcium and phosphorus metabolism? What does that mean for eggshell quality?
[Dr. Kathrin Bühler] Calcium and phosphorus are key elements for various functions in the body and thus need to be closely regulated. To maintain their homeostasis, there is a close interaction among the intestine (absorption), the kidney (excretion and reabsorption) and the bones (deposition for storage and resorption). One of the key players in this interaction is vitamin D, more precisely its bioactive form 1,25(OH)2D3.
In the laying hen, an additional factor in calcium homeostasis is the eggshell, which daily requires the deposition of approximately 2.2 g of calcium. Because of this, any disturbance in calcium and – to a lesser extent – phosphorus metabolism immediately leads to disturbances in eggshell formation and loss of bone tissue. Vitamin D metabolism is a key factor regulating the homeostasis of these two minerals.
Dr. Sabrina Autzen
Lead R&D – Plant Sciences
[Feedinfo] Dr. Autzen, why does Herbonis believe Solanum glaucophyllum is “the unique plant to support eggshell formation”?
[Dr. Sabrina Autzen] This is thanks to 1,25-dihydroxycholecalciferol, which – as mentioned by my co-authors – regulates intestinal, renal and bone metabolism to deliver enough calcium ions for eggshell formation. In certain cases, for example with aging laying hens, supplementation with 1,25-dihydroxycholecalciferol is necessary to meet the animals’ requirement, as aged laying hens lack the kidney enzyme to efficiently activate 25(OH)D into 1,25-dihydroxycholecalciferol.
Nature provides Solanum glaucophyllum as an excellent answer for these needs. This plant contains 1,25-dihydroxycholecalciferol in glycosidic form. After ingestion, 1,25-dihydroxycholecalciferol is enzymatically released and becomes available for absorption. Only a few other plants are known to contain 1,25-dihydroxycholecalciferol, however, S. glaucophyllum contains the highest concentration in glycosidic form, which is particularly high in Herbonis’ variety Hervit 153.
[Feedinfo] Tell me about Hervit 153, a protected variety of Solanum glaucophyllum. How is it different from wild-type waxy-leaf nightshade in ways that are interesting for its use in feed?
[Dr. Sabrina Autzen] Compared to its wild-type ancestor, Hervit 153 offers several advantages. The most important being enhanced leaf yield combined with an increased level of 1,25-dihydroxycholecalciferol. Additional benefits include crop yield uniformity and disease resistance. Our customers require consistent quality. Hervit 153 is free of undesired substances and therefore can be used in animal feed after drying, grinding and standardization. No additional treatments are needed.
Beyond the uniqueness of this genetic variety of S. glaucophyllum, Herbonis has also designed growing conditions for the plant to optimise for its application in feed. The most important factors for any plant growth, and especially for the concentration of secondary plant metabolites, are certainly specific conditions of soil, water, temperature, and light. Here, light means, for example, in the right wavelength, duration and intensity. Only the optimum combination with the right genetic resource leads to favored and constant amounts of 1,25-dihydroxycholecalciferol glycosides, something which Herbonis has mastered.